Study on the doping mechanism of chromium in nano-sized iron oxide

Nano - sized Fe2O3 containing 0 similar to 14% (mass fraction) Cr2O3 was pr epared by coprecipitation method using Fe3+ (Cr3+)/Fe2+ mixed ions (with th e ions ratio = 2:1.). XRD Rietveld analysis showed that such Fe2O3 was a mi xture of crystalline gamma - Fe2O3 and amorphous Fe2O3. The abundance of am orphous Fe2O3 ranged from 21.72% to 48.60%. When the amount of doping Cr2O3 was less than 2.4%, the Mossbauer spectra of either the crystalline or amo rphous Fe2O3 samples were all sextets. If Cr2O3 was more than 2.4%, there a ppearred a superpara - magnetic doublet whose intensity increases linearly with the concentration of Cr2O3. During coprecipitating, there existed two hydrous complexes, one was Fe3+ hydrous complexes mixed with a small amount of Cr3+, another was Cr3+ hydrous complexes mixed with Fe3+. These hydrous complexes formed nano - sized magnetic and non - magnetic Fe2O3 respective ly. The later hydrous complexes mixed with the former, hinderd crystal form ing and growth.